Sight level indicators are suitable for visual inspection of liquid levels in vessels for many applications. For instance, such a sight level indicator may indicate oil level in an oil reservoir, fuel level in a fuel tank or water level in a boiler. Such sight level indicators that are in current use rely on a visible scale that is generally perpendicular to the surface of the liquid and has scale gradations on it that indicate the liquid level.
Such sight level indicators lend themselves well to mounting on a side of the liquid vessel. The scale gradations representing level are then clearly visible. However, in applications where side mounting of sight level indicators are not possible, top mounted sight level indicators are necessary. In these instances, such top mounted indicators generally have optical systems that make the perpendicular scale gradations visible from above the surface of the liquid. For instance, a prism or a mirror system may be suitable for this purpose.
However, such optical systems add to cost and they are subject to contamination by the liquid. A top reading liquid sight glass that can read the liquid level without such optical systems would be a great improvement.